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Assessment of a genetic breeding control strategy for scrapie
G. Nodelijk, H. J. W. van Roermund, L. J. M. van Keulen, B. Engel, P. Vellema, T. J. Hagenaars
SCRAPIE control policies, based on selecting animals with a scrapie-resistant genotype (ARR/ARR) for breeding, have been adopted by a number of countries in Europe. This study assessed the effectiveness of such a breeding programme in classical scrapie-affected sheep flocks in the Netherlands.
Six commercially run sheep farms with a recent history of confirmed cases of scrapie were selected for the study in 2000, and were enrolled for four to six years. Each flock had approximately 90 to 100 sheep, and only ARR/ARR rams were used for breeding. All breeding animals were genotyped at the start of the study, as well as offspring and rams purchased in subsequent years. Tonsil samples were collected yearly from all breeding sheep and tested for the pathogenic isoform of the prion protein (PrPSc). All animals that were culled or died were tested for the presence of PrPSc in tonsil or brain tissue. Mathematical modelling was used to analyse monitoring data from four flocks, to quantify how the transmission risk in a flock changed over time.
Results from 1175 sheep …